A variety of restraint systems have been devised for vehicle occupant safety. The most commonly employed systems have belts or harnesses to fasten about vehicle occupants as well as inflatable air bags. These systems have been fairly effective in controlling occupant motion and absorbing the occupant's kinetic energy.
Both upper and lower body safety can be achieved by purely "passive" restraint systems. In this context, "passive" refers to the requirement that the occupant not have any active participation in the deployment or application of the restraint system once the occupant is seated in the vehicle. This is currently achieved by using automatically applied seat belts and automatically actuated air bags and knee bolsters. One such passive restraint system includes is an air bag to protect the upper torso and head and a knee bolster to provide lower torso restraint.